This invention relates to positioning systems and particularly to means for positioning knitting machine guide bars.
Knitting machines usually have at least two guide bars. Each bar supports guides in the form of blades with eyelets through which warps are threaded. Each guide controls movement of the warps relative to the needles of the machine. It is the function of the guide bars to move the warps quickly to predetermined locations corresponding to the spaces between needles.
In many warp knitting machines the guide bars are moved by cams. Common cylindrical cams are used for short programs where the pattern repeats after 16 or 24 machine cycles. Longer programs are contained in chains. The height or thickness of each link determines the position of cam followers and consequently the guide bars. A chain is required for each guide bar. Although these chains are made up to 60 feet long, they are unable to contain some desirable programs.
Changing the machine from one knitting pattern to another usually involves changing cylindrical cams or chains. This is comparatively difficult. Also the chains are costly and if the required links are not available from stock at the knitting mill, there may be a delay while missing links are obtained.
Most tricot warp knit machines have needle spacings of 20, 24, 28, or 32 needles per inch. When changing from one spacing to another, the increments and positions of the guide bars must change accordingly. The changing of cams or chains is comparatively difficult and time consuming.
Also, cams only provide short programs. With chains it is difficult to move the pattern bars smoothly because of abrupt changes which occur between links. Thus, chain machines have limited speed capabilities.
Guide bars commonly require one or more sets of heavy springs which oppose the action of the cams, followers, and connecting rods used for positioning the guide bars. The spring forces must always exceed the forces of friction and inertia, both of which can reach high peaks at times. These springs function as a means of taking slack out of the entire train of elements in the positioning system. However, the spring forces which are always higher than the highest momentary opposing force cause wear in the several parts that are stressed by the springs. Furthermore, the springs are often decentered with respect to the main body of the guide bar. Thus they exert bending forces which tend to throw the bars and individual guides out of line.
The needles in such machines are spaced as close as 0.030 inch on centers. These must pass between guide blades which have warps threaded through their eyelets. Thus high accuracy is required for positioning the guide bars. Such high accuracy is needed to operate with the very slight clearances between the needles and guide bars.
An object of the present invention is to improve positioning systems, particularly for knitting machines.
Another object of this invention is to overcome the before-mentioned problems.